Clutch unit

ABSTRACT

A clutch unit especially adapted for accurately controlling the transmission of high rotary forces with minimum residual drag. A servo control valve supplied with hydraulic fluid by a pump controls a first stage fluid amplifier supplied by a separate pump, this amplifier in turn controlling a second stage amplifier supplied by a third pump. The second stage amplifier supplies main and auxiliary inlet ports of the clutch unit. The oil shear type clutch has a plurality of interleaved plates and discs. Separate piston and cylinder means are provided for actuating the plates for each clutch disc by means of the main fluid supply, the pressure of which is varied in accordance with input signals to the servo control valve. The auxiliary supply to the clutch acts both to retract the piston and cylinder means, thus separating the plates and discs with a minimum of residual drag, and as a cooling medium. The clutch discs are segmented so as to permit economical fabrication in spite of the large size of the clutch, with the disc segments being mounted so as to permit convenient replacement without requiring complete disassembly of the unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to clutch units of the oil shear type, andparticularly to units having interleaved clutch plates and discs whichare alternately clamped together or separated in an axial direction. Theinvention is directed toward a very large size clutch unit such as wouldbe found in an aircraft catapult system for selectively winding ortensioning a nylon belt or tape which is in turn connected to a carriagesecured to the aircraft to be launched or catapulted.

2. Description of the Prior Art

My U.S. Pat. No. 3,696,898 issued Oct. 10, 1972 shows a clutch-brakeunit in which a plurality of interleaved clutch discs and plates areprovided, all of which are simultaneously actuated by a single piston.The arrangements shown in this patent would be unsatisfactory for thepurpose of actuating large size clutch units which must transmit highhorsepowers. Among the problems to be dealt with in the construction oflarge size oil shear type clutch units are the need for maximumapplication of forces to couple the plates and discs, the coolingrequirements for the parts, and most importantly, the need forminimizing residual drag. To illustrate the magnitude of residual dragproblems, it should be noted that in an 85,000 horsepower clutchoperating at 1200 R.P.M., the residual drag is in the order of 8-10,000horsepower. The residual drag in the apparatus of the present invention,on the other hand, is less than 500 horsepower.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel and improvedclutch unit which overcomes the disadvantages of previously knownconstructions, especially when applied to large size power transmissionrequirements.

It is another object to provide an improved oil shear type clutch unitof this nature which is capable of applying strong coupling forcesbetween the plates and discs while still maintaining high controlaccuracy in accordance with various input conditions.

It is a further object to provide a novel and improved clutch unit ofthis nature which utilizes hydraulic fluid for the dual purpose ofretracting the plate actuating means to reduce residual drag, and as acoolant for the clutch discs.

It is also an object to provide an improved clutch unit of thischaracter in which replacement of portions of the clutch discs may beeffected without requiring complete disassembly of the unit.

Briefly, the clutch unit of this invention comprises an input shaft, anoutput shaft, a plurality of clutch plates connected to one of saidshafts, a plurality of clutch discs interleaved between said clutchplates and connected to the other shaft, and separate means for closingthe gap between each clutch disc and its adjacent clutch plates, saidmeans comprising piston and cylinder means connected to said clutchplates on opposite sides of each clutch disc, and fluid pressure controlmeans for simultaneously supplying pressurized fluid in parallel to allof said piston and cylinder means. As will hereinafter be described, theprovision of the separate piston for each of the disc segments minimizesresidual drag of the unit. Auxiliary fluid pressure control means areprovided for said piston and cylinder means acting in a directionopposite to said first-mentioned fluid pressure control means for urgingsaid clutch plates to retract from said clutch discs. Conduit means arefurther provided for said auxiliary fluid pressure control means leadingfrom said piston and cylinder means to the vicinity of an adjacentclutch disc whereby said auxiliary fluid will act as a coolant.

In another aspect, the clutch unit comprises an input shaft, an outputshaft, a plurality of clutch discs connected to one of said shafts, aplurality of clutch plates interleaved with said discs and connected tothe other shaft, said clutch discs extending outwardly from said clutchplates, each of said clutch discs comprising a plurality of arcuatesegments in a circumferential arrangement, longitudinally extendingsupporting means for clutch disc segments, coacting portions on saidsupporting means and the edges of said clutch disc segments for holdingthe segments in position, and removable fastener means for holding saidsupporting means in position, whereby removal of said fastener meanswill permit one or more segments to be separately removed from saidclutch unit without disturbing the other segments. It is to be notedthat clutch discs of the type utilized herein are traditionallymanufactured through the use of relatively small size retort equipment,and that such equipment is not readily available for use in fabricatinglarge diameter clutch components. Consequently, by utilizing relativelysmaller size clutch disc segments, the conventional retort equipment maybe employed.

In still another aspect, the invention comprises an oil shear typeclutch having interleaved clutch plates and clutch discs, each of saidclutch discs comprising a plurality of arcuate segments in acircumferential arrangement, shafts for said plates and discs, and meansmounting said segments on their shaft whereby said segments areseparately removable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a stored energy rotary driveaircraft catapult with which the present invention is associated;

FIG. 2 is a block diagram showing the components of the system forcontrolling the clutch unit;

FIG. 3 is a cross-sectional view of the servo control valve and firststage amplifier;

FIG. 4 is a cross-sectional view of the second stage amplifier;

FIG. 5 is a partially sectioned side elevational view of the clutchunit;

FIG. 6 is a cross-sectional view in elevation taken along the line 6--6of FIG. 5 and showing the input shaft, a bearing, and the housing;

FIG. 7 is an enlarged cross-sectional view in elevation taken in thearea marked 7 of FIG. 5 and showing the construction of the piston andcylinder means for a pair of clutch plates; and

FIG. 8 is a cross-sectional view taken along the line 8--8 of FIG. 7 andshowing the means for removably supporting the clutch disc segments.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The clutch unit of this invention is shown generally at 11 in FIG. 1 aspart of a stored energy rotary drive catapult, for example, one whichwould be used in an aircraft catapult system. Such a system has a primemover such as a turbine 12 having a flywheel 13 and connected throughreduction gearing 14 to drive clutch unit 11. The output shaft of driveclutch 11 is connected to a tape reel 15, the other side of this tapereel being connected to a reel brake 16 which does not form part of thepresent invention. The tape reel is used for selectively winding ortensioning a nylon belt or tape 17 which in turn is connected to acarriage 18 secured to the aircraft to be launched or catapulted. Anadvanced motor 19 is provided for returning carriage 18 to its startingposition.

The clutch operating system is shown schematically in FIG. 2 andcomprises a servo control valve generally indicated at 20, a first stagefluid amplifier generally indicated at 21, a second stage fluidamplifier generally indicated at 22, and clutch unit 11. A reservoir 24is shown in FIG. 2 and is adapted to supply fluid to three pumps, 25, 26and 27 for servo control valve 20, first stage amplifier 21, and secondstage amplifier 22 respectively. It has been found that three separateflows are necessary from the three separate pumps 25, 26 and 27 in viewof the fact that each flow requires a different flow rate and pressure.

The purpose of the servo control valve is to provide extremely accuratefluid pressure control in response to various conditions. For example,in the case of a catapult system, the torque output of the clutch mustbe profiled in accordance with wind and temperature conditions as wellas the type of aircraft being launched. The servo valve 20 is shown morespecifically in FIG. 3 and is of the same general type shown anddescribed in my U.S. Pat. No. 3,851,742 issued Dec. 3, 1974. The servocontrol valve has a main body 28 and a coil housing 29. Coil leads 30extend into main body 28 and are connected to a 12-volt d.c. coil 31 incoil housing 29. This coil controls the movement of a disc 32 whichfaces a valve seat 44 (hereinafter to be described) and is drawn towardsaid valve seat with a force depending upon the current passing to thecoil. Pump 25 is connected to an inlet port 35 in main body 27, and apassage 36 extends through body 27 from this port. A passage 37 leads atright angles from passage 36 through coil 31 to disc 32, the member 38in which passage 37 is formed extends through opening 34 and issealingly connected thereto by an O-ring 39. The disc 32 is held by aguide 40 formed as a part of an end body 41 and disposed in a chamber 42of coil housing 29, and an outlet port 43 is connected to this chamber.The position of disc 32 with respect to the valve seat 44 formed at theend of passage 37 thus controls the fluid flow from inlet port 35 tooutlet port 43 which is connected to reservoir 23.

The end of passage 36 opposite inlet port 35 is connected to a signalport 45 formed in first stage amplifier 21. A piston 46 is slidablymounted in the first stage amplifier which is made up of two bodysections 47 and 48 secured together by bolts 49. Piston 46 faces an endcap 51 on the first stage amplifier and forms therewith a chamber 52.This chamber is connected with port 45 by a passage 53, a restriction 54and recessed portions 55 on piston 46 which engage a shoulder 56 on endcap 51.

A helical coil compression spring 57 is mounted in body section 48 ofthe first stage amplifier and engages an adjustable member 58 carried bypiston 46, urging the piston against shoulder 56. A valve 59 is formedon the end of piston 46 opposite that which engages shoulder 56. Thisvalve is tapered and co-acts with a correspondingly tapered valve seat61 on body section 48. An inlet port 62 is formed in body section 48 ofthe first stage amplifier and is connected with the outlet of pump 26. Apassage 63 leads from inlet port 62 to valve seat 61. According to theamount of pressure in chamber 52, piston 46 will close to a greater orlesser extent the gap between its valve 59 and valve seat 61, thuscontrolling the pressure of the fluid communicated via the inlet port68. Valve seat 61 leads to a chamber 64 which in turn has a passage 65leading to an outlet port 66 which is connected to the reservoir 23.Another passage 67 leads from inlet port 62 in the opposite directionfrom passage 63. Passage 67 leads to a passage 68 in the oil manifold 69of second stage amplifier 22. Thus, the amount of pressure delivered tothe signal port of the second stage amplifier will be controlled by theposition of piston 46 which is in turn controlled by the position ofdisc 32.

The construction of second stage amplifier 22 is shown in FIG. 4 whichalso indicates the manner in which the servo control valve and firststage amplifier are connected thereto. The second stage amplifiercomprises an elongated body 71 having an inlet port 72 at its midportionand extending transversely thereto into a central chamber 73. Inlet port72 is supplied by pump 27, and passage 73 has a pair of tapered valveseats 74 and 75 at its opposite ends and facing in opposite directions.An end member 76 is mounted in housing 71 and has a cylinder 77 formedtherein. A piston 78 is slidably mounted in this cylinder and is securedto one end of a piston rod 79 slidably mounted in member 76. The otherend of this piston rod carries a valve 81 which co-acts with valve seat74 to control the amount of fluid flowing from passage 73 into a chamber82 which surrounds a reduced portion 83 of end member 76. An outlet port84 leads from chamber 82 to reservoir 23. A plurality of springs 85 urgevalve 81 in a direction closing the space between seat 74 and valve 81.Signal port 68 is connected to a chamber 86 formed by piston 78 and oilmanifold 69, and pressure in this chamber will move valve 81 along withthe action of springs 85 to restrict the passage to valve seat 74.

A valve 87 is disposed adjacent valve seat 75 and is guided for axialmovement by an end member 88 in body 71. The valve is held normallyclosed by a plurality of compression springs 89 disposed in bores withinmember 88. However, when the pressure within chamber 73 reaches apredetermined magnitude, valve 87 will be lifted from seat 75 to permitfluid to pass through the valve seat.

Valve seat 75 leads to a chamber 91 which has an outlet port 92connected to an inlet passage 93 (FIG. 5) for the clutch unit. Passage93 constitutes the main fluid supply connection for the clutch unit and,as will be later described, supplies fluid which simultaneously actuatesall the clutch plate piston and cylinder means in a coupling direction.An axial bore 94 in valve 87 leads to a chamber 95 within end member 88.An outlet port 96 leads from chamber 95 to a passage 97 in the clutchunit (FIG. 5). Passage 97 constitutes a auxiliary fluid supply for theclutch unit, the fluid in this passage exerting constant retractingpressure on the clutch plate piston and cylinder means as well asserving a cooling function for the clutch discs. A tapered seat 98 isprovided in the end passage 94 which co-acts with a complementaryadjustable valve 99. The position of valve 99 may be preselected todetermine the flow rate and pressure to the auxiliary passage 97. A sidepassage 101 leads from passage 94 to a chamber 102 on the side of valve87 opposite that which faces chamber 73. The pressure in chamber 102aids springs 89, but the area on which the pressure in chamber 102 actsis less than that on which the fluid in chamber 73 acts in a valveopening direction.

FIGS. 5-8 shows the construction of clutch unit 11. The clutch unitcomprises a base 103, a lower housing 104 (which is preferably formedintegrally with base 103), and a domed upper housing 105. An input shaft106 extends through an end plate 107 at one end of the housing and anoutput shaft 108 extends through an end plate 109 at the other end.Input shaft 106 is supported by a hydrodynamic bearing 110 and by ahydrostatic bearing 162 hereinafter to be described. Output shaft 108 isrotatably supported by hydrostatic bearings 111 and 112 which haveseparate oil supplies.

A housing 113 surrounds bearing 110 so as to journal support theadjacent end of the input shaft 106. The housing 113 defines an annularchamber 114 which is supplied by main fluid inlet passage 93. A secondand smaller annular chamber 115 in housing 113 is supplied by auxiliaryfluid passage 97. It should be noted that the bearing 110 acts as arotary fluid seal between the chambers 114 and 115.

A radially outwardly extending portion 116 is formed on the end of inputshaft 106 within housing 104, 105 and has a plurality of radial passages117. An annular member 118 is disposed within a bore in shaft 106 andextends between chamber 114 and passages 117. A plurality of inwardlyextending radial passages 119 extend from annular chamber 114 and areconnected to the axially extending chamber 121 formed by member 118 andshaft 106. Thus, the main fluid flow will be led radially outwardly bypassages 117. It should be noted that input shaft 106 with portions 116,members 122 and 161 (hereinafter described), form a unitized input shaftassembly.

An annular member 122 is provided and extends axially from the outeredge of input shaft portion 116. A plurality of circumferentially spacedaxially extending passages 123 are formed in member 122. One end of eachpassage 123 is connected to a corresponding radial passage 117 by ashort connecting passage 124.

A plurality of annular clutch plate assemblies generally indicated at125 are secured in axially adjacent relation to the outside of member122. The assemblies are held in position by key 126 on member 122 so asto prevent relative rotation, and are held against endwise movement byannular members 127 and 128 carried by the ends of member 122. Theconstruction of each assembly 125 is shown in detail in FIGS. 7 and 8.The clutch assembly comprises an inner member 129 mounted on key 126 andhaving fitting spacers 131 at opposite ends which maintain properspacing with respect to the adjacent assemblies 125. One portion ofmember 129 is provided with splines 132. A first annular clutch plate133 of L-shaped cross section has splines 134 interfitting with splines132. The main radially extending portion of clutch plate 133 has a heattreated surface 135 engageable with one side 136 of a series ofsegmented annular clutch discs 137 which are described in detail below.A piston 138 is threadably mounted at 139 on the portion of clutch plate133 which carries splines 132. The piston is slidably mounted within acylinder 141 which has a first radially extending portion 142 slidablyconnected by splines 143 to splines 132. A second axially extendingportion 144 of member 142 has a second annular clutch plate 145 securedthereto by a plurality of circumferentially spaced bolts 146. Clutchplate 145 has a heat-treated surface 147 engageable with the other side148 of clutch disc segments 137.

Fluid passage means are provided for leading the pressurized fluid frompassage 123 to the chamber 149 which is formed between clutch plate 145and piston 138. A seal 151 is carried by the axially extending portionof clutch plate 133 and engages a facing surface on clutch plate 145,and a seal 152 carried by piston 138 engages cylinder 141, these twoseals forming the closed chamber 149. The passage means comprises aradial passage 153 leading from passage 123 to a passage 154 in member129. A passage 155 in the axially extending portion of clutch plate 133leads from passage 154 to chamber 149. Passages 157 are formed in thepiston 138 to provide fluid flow between passage 155 and the interior ofthe chamber 149. A plurality of control orifices 158 extend through theaxially extending portion of clutch plate 133 to the space 159 in thevicinity of clutch disc segments 137. These control orifices lead frompassage 154 and are for cooling fluid to the clutch disc segments.

A radial plate 160 is secured to the inside of member 122, and a bearingsupport section 161 is secured to the central portion of plate 160 andcarries the aforementioned hydrostatic bearing 162. This bearing permitsthe extension 163 secured to the inner end of output shaft 108 tojournal support section 161 and hence rotatably support inner end of theshaft 106.

Annular chamber 115 for the auxiliary fluid feeds a radially inwardlyextending passage 164 in shaft 106 which leads to an axial passage 165.The auxiliary fluid will flow from this passage through a centralpassage 166 in member 118 to radial slots 167. This passage leads to anannular chamber 168 formed between an end flange member 169 mounted onmember 118, and a chamber on shaft portion 116. Flange 169 is secured bybolts 170 to shaft portion 116. Passages 171 lead from chamber 168 toradial passages 172 in shaft portion 116 between passages 117.

Passages 172 lead to a plurality of axial passages 173 disposed betweenpassages 123 in member 122. A radial passage 174 leads from each passage173 to an annular chamber 175 in each member 129. Chamber 175 is locatedalongside chamber 154 but is of somewhat small cross-sectional area. Oneor more restricted passages 176 lead from chamber 175 to cylinderchamber 141. Pressure in chamber 141 caused by the centrifugal force ofthe oil within the unit will tend to move clutch plates 133 and 145 awayfrom clutch disc segments 137. The auxiliary fluid will thus serve thefunction of constantly and positively urging retraction of the clutchplates, so that when pressure is relieved in chamber 149, the clutchplates will be entirely separate from the clutch discs to reduceresidual drag to a minimum.

A passageway 177 leads from each chamber 141 through member 142 to anextension 178 loosely interfitting with a recess 179 in the adjacentclutch plate 133. A passage 180 leads from chamber 179 through clutchplate 133 to the space 159 surrounding disc segments 137. The auxiliaryfluid will thus serve the additional function of cooling the clutchdiscs both during the operation of the unit and when the clutch isdisengaged.

An outwardly radial portion 181 is formed on output shaft 108 betweenbearings 112 and 162. Portion 181 is located at one end of the stack ofclutch plates and discs. A member 183 is disposed at the other end ofthe stack and extends radially inwardly, the inner end 184 of thismember extending axially and being supported by bearings 111.

The series of segmented clutch discs 137 are mounted in such a manner asto permit the easy removal of replacement of individual segments withoutthe necessity of disassembling the entire mechanism. This meanscomprises recessed portions 185 on the opposite edges of each clutchdisc segment 137 which interfit with bushings 192. These bushings haveshoulders 196 which engage the sides of the clutch disc segments. Thespacing between shoulders 196 at the opposite ends of the bushings 192will allow slight axial play of the clutch disc as seen in FIG. 7. Theupper surfaces 197 of bushings 192 are flat so as to be engageable bykeys 191 and the portions 201 of shoulders 196 opposite surfaces 197 arealso flat.

Keys 191 are slidable into enlarged portions 188 on rings 186 and 187which surround the clutch discs, these enlarged portions having slots189 to receive members 191. Each pair of rings 186 and 187 is connectedby bridges 182 between sets of clutch disc segments. These are thus aplurality of integral members in tandem, each comprising a ring 186, aring 187, and connecting bridges 182. The facing rings 186 and 187between adjacent integral members clamp bushings 192 between them. Theclamping is accomplished by studs 193 with nuts 194 and 195, the nutsbeing disposed between bridges 182. The studs at the ends of the stackare secured to members 181 and 183 as seen in FIG. 5. Members 191 arealso held between these rings and are further secured againstcircumferential movement by locking bolts 198 passing through members199 which are secured to rings 186 or 187 and threaded into members 191.

It will thus be seen that removal and replacement of any one or more ofclutch disc segments 137 may be easily affected without the necessity ofdisassembling the entire unit. It will merely be necessary to unscrewthe desired bolts 198, slip out members 191 from the raised portions 188of rings 186 and 187 and rotate members 192 on their own axes until flatportions 197 and 201 face one another, i.e., are opposite the recessedportions 185 of the clutch disc segments 137. One may then slip out theclutch disc segment(s) since lips 196 will no longer be blocking suchremoval. After the new clutch disc segment(s) are inserted, members 192may be rotated to their original position so that their lips 196 holdthe new clutch segment(s) in place and members 191 slipped into positionand held in place by bolts 198.

In operation of the entire system, the input signal to solenoid 31 ofservo control valve 20 will cause this valve to control the signal tofirst stage fluid amplifier 21. This in turn will control the signal tosecond stage fluid amplifier 22, thus determining the flow rate andfluid pressure of both the main and auxiliary supplies to clutch 11. Themain fluid supply will be fed to chambers 149 of piston and cylindermeans 138, 141 of all the clutch assemblies 125. Thus, clutch plates 133and 145 will approach the clutch disc segments 137 disposed between themto a greater or lesser extent depending upon the pressure supplied tochambers 149. Since the pressure is simultaneously applied in parallelto all chambers 149, the separate piston and cylinder means for each setof clutch disc segments and clutch plates will impose full force on allportions of the assembly, permitting the transmission of maximum torque.

At the same time fluid will be flowing through the auxiliary passagesand out through passages 180 to the space 159 adjacent the clutch discsegments, while the main fluid supply will pass through orifices 158 tomaintain the cooling effect on the clutch disc segments.

Since the auxiliary oil supply maintains a pressure in chambers 141 inaccordance with the rotational speed of the unit (magnitude of thecentrifugal force acting on the oil) the piston and cylinder means willbe caused to positively retract, separating clutch plates 133 and 145from the clutch disc segments and reducing to a minimum the residualdrag.

It will be seen from the foregoing that the present invention provides anew and improved clutch unit which has a number of extremely importantfeatures not shown in the prior art. Among the more important of thesefeatures is highly improved cooling through better oil flow control, anda minimum amount of disc friction on the disc stack which provides forimproved torque control. Another extremely important feature of thepresent invention is the segmental disc arrangement which minimizes thedeleterious effects of heat on the discs. Additionally, convenientinspections of the disc segments is achieved without requiring total"tear-down" of the unit. Another feature of the present inventionresides in the fact that retraction of the discs is achieved via thecentrifugal force of the oil which obviates the need for retractionsprings which might tend to malfunction in clutch units of the size andspeed range of the applicant's invention. More importantly, however, thepresent invention provides a new and improved clutch unit whichminimizes residual drag which is extremely important in clutch units ofthe capacity, i.e., 85,00 h.p., of the present invention.

While it will be apparent that the preferred embodiment of the inventiondisclosed is well calculated to fulfill the objects above stated, itwill be appreciated that the invention is susceptible to modification,variation and change without departing from the proper scope or fairmeaning of the subjoined claims.

I claim:
 1. A clutch unit comprising an input shaft, an output shaft, aplurality of clutch plate elements connected to one of said shafts, aplurality of clutch disc elements interleaved betwen said clutch plateelements and connected to the other shaft, and separate means forclosing the gap between each clutch disc element and its adjacent clutchplate element, said means comprising piston and cylinder meansassociated with one of said plurality of clutch plate elements andclutch disc elements, and fluid pressure control means forsimultaneously supplying pressurized fluid in parallel to all of saidpiston and cylinder means.
 2. A clutch unit according to claim 1,further provided with auxiliary fluid flow system means for said pistonand cylinder means acting in a direction opposite to saidfirst-mentioned fluid pressure control means for urging said clutchplate elements to retract from said clutch disc elements.
 3. A clutchunit according to claim 2, further provided with passageway means fordiverting fluid to the vicinity of the clutch disc elements for coolingpurposes.
 4. A clutch unit according to claim 2, further provided withpassageway means leading from said auxiliary fluid flow system means tothe vicinity of an adjacent clutch disc element for cooling purposes. 5.A clutch unit according to claim 1, said piston and cylinder meanscomprising a cylinder secured to one clutch plate element adjacent theclutch disc element and a piston secured to the other clutch plateelement, said fluid pressure control means comprising main flowpassageway means conducting pressurized fluid to one side of the pistonso as to cause said clutch plate element to engage said clutch discelement.
 6. A clutch unit according to claim 1, each of said clutch discelements comprising a plurality of circumferentially arranged clutchdisc segments, and means for supporting said clutch disc segments forremoval independently of each other.
 7. A clutch unit according to claim1, said one shaft having an axially extending portion carrying aplurality of said clutch plate elements, said fluid pressure controlmeans including passageway means through said axially extending portionof said one shaft.
 8. A clutch unit according to claim 7, said axiallyextending portion of the one shaft having a plurality of axiallyextending passages, some of said passages being for main fluid pressureflow and alternate passages being for auxiliary fluid system flow, achamber carried by said one shaft, means supplying auxiliary fluid flowto said chamber, and radial passages leading from said chamber to saidalternate axial passages.
 9. A clutch unit according to claim 1, saidfluid pressure control means comprising a servo control valve, a firststage fluid amplifier connected to the output of said servo controlvalve, and a second stage fluid amplifier connected to the output ofsaid first stage fluid amplifier, said piston and cylinder means beingconected to the output of said second stage fluid amplifier.
 10. Aclutch unit according to claim 9, further provided with a reservoir andthree separate pump means between said reservoir and said servo controlvalve, said first stage fluid amplifier and said second stage fluidamplifier.
 11. A clutch unit comprising an input shaft, an output shaft,a plurality of clutch plates connected to one of said shafts, aplurality of clutch discs interleaved between said clutch plates andconnectd to the other shaft, means for decreasing the gap between theclutch discs and the clutch plates, said decreasing means includingfluid pressure control means for applying fluid pressure to saiddecreasing means, means for increasing the gap between said clutch discsand clutch plates, and centrifugal fluid pumping passage means forsupplying fluid under pressure exerted by the centrifugal forcedproduced by rotation of the unit to said increasing means whereby saidincreasing means are operative to increase the gap between said clutchdiscs and said clutch plates in response to release of fluid pressure onsaid decreasing means.
 12. A clutch unit comprising an input shaft, anoutput shaft, a plurality of clutch plate elements connected to one ofsaid shafts, a plurality of clutch disc elements interleaved betweensaid clutch plate elements and connected to the other shaft, actuatingmeans for moving said clutch plate elements and said clutch discelements into torque transmitting relationship, and fluid pressurecontrol means for controlling said actuating means, said fluid pressurecontrol means including servo control valve means and fluid amplifiermeans, said fluid amplifier means include a first stage fluid amplifierconnected to the output of said servo control valve and a second stagefluid amplifier connected to the output of said first stage fluidamplifier, said servo control valve means being operative to control theoutput of said fluid amplifier means, the output of said second stagefluid amplifier being connected to said actuating means so as to controloperation thereof.
 13. A clutch unit comprising an input shaft, anoutput shaft, a plurality of clutch plate elements connected to one ofsaid shafts, a plurality of clutch disc elements interleaved betweensaid clutch plate elements and connected to the other shaft, said discelements and said plate elements defining gaps therebetween, primaryfluid flow paths for supplying fluid to said gaps for cooling andlubricating said disc elements and said plate elements and auxiliaryfluid flow paths for supplying fluid to said gaps independently of saidprimary fluid flow path, said auxiliary fluid flow paths being operativeto supply fluid to said gaps during both operation and disengagement ofsaid clutch.
 14. A clutch unit according to claim 13 wherein each ofsaid plurality of disc elements and associated clutch plate elements hasa primary fluid flow path and auxiliary fluid flow path associatedtherewith.